Method and device for detecting rate

ABSTRACT

Device for determining the rate of a received communication frame, including a plurality of encoded signal quality estimators, each at a different rate, a decision controller, connected to the encoded signal quality estimators, a decoder connected to the controller and an erasure detection unit connected to the decoder and the controller, wherein each of the quality estimators processes the received encoded frame according to an encoded signal quality criteria, thereby producing a quality value, wherein the controller selects the rate with the best quality value, the decoder decodes the encoded frame according to the selected rate and the erasure detection unit analyzing the decoded frame, thereby determining it as allowed or as erased.

FIELD OF THE INVENTION

The present invention relates to a method and system for detecting anddetermining the data rate of a received signal, in general and to amethod and system for providing an appropriate data rate and erasuredecision, in particular.

BACKGROUND OF THE INVENTION

In the art, there are known methods and systems for determining the datarate of a received signal. Communication standards often addressproblems of variable bandwidth due to interference reflections, speechactivity controlling and the like, by providing several modes oftransmission, each in a predetermined data rate.

The definition of the basic terms used hereinbelow can be found in"CDMA--principles of spread spectrum communication", by A. J. Viterbi,Addision-Wesley Publishing Company, 1995.

Reference is now made to FIG. 1 which is a schematic illustrating of asystem, referenced 1, known in the art. System 1 receives an incomingsignal, which has been transmitted at a rate, selected from a set ofrates. In the present example, the rate set includes four rates. Therates are, marked 1, 1/2, 1/4 and 1/8. The maximal volume of informationwhich can be transmitted in rate 1/2 is half the maximal volume ofinformation which can be transmitted in rate 1. The same applies forrates 1/4 and 1/2, and rates 1/8 and 1/4, respectively.

System 1 includes a plurality of decoding and estimating units 2, 4, 6,and 8 for each available rate. Unit 2 includes a decoder 10 and areception quality estimator 12, which is connected to the decoder 10.Unit 4 includes a decoder 14 and a reception quality estimator 16, whichis connected to the decoder 14. Unit 6 includes a decoder 18 and areception quality estimator 20, which is connected to the decoder 18.Unit 8 includes a decoder 22 and a reception quality estimator 24, whichis connected to the decoder 22.

System 1 further includes a decision controller 26 which is connected tounits 2, 4, 6 and 8.

The received encoded signal is provided to each of the decoding andestimating units 2, 4, 6, and 8. The decoder 10 decodes the encodedsignal according to rate=1 and provides the decoded signal to thereception quality estimator 12. The reception quality estimator 12processes the decoded signal so as to produce a quality value andprovides it to the decision controller 26.

The decoder 14 decodes the encoded signal according to rate=1/2 andprovides the decoded signal to the reception quality estimator 16. Thereception quality estimator 16 processes the decoded signal so as toproduce a quality value and provides it to the decision controller 26.The same process is executed by units 6 and 8 so as to produce qualityvalues for rates 1/4 and 1/8, respectively.

Then, the decision controller 26 selects the rate which has best qualityvalue and informs the receiver that the received encoded signal is to beprocessed according to the selected rate. Such systems are described inseveral U.S. patents.

U.S. Pat. No. 5,230,003 to Dent et al describes a method which decodes areceived signal according to two rates, thereby producing two decodedsamples, provides a quantitative measurement for each of these decodedsamples, compares between the quantitative measurements and selects arate accordingly.

U.S. Pat. No. 5,566,206 to Butler et al describes a method which decodesa received signal according to plurality of rates, re-encodes all of thedecoded samples, counts the number of symbol errors, combines qualityestimation and selects the rate accordingly.

U.S. Pat. No. 5,671,255 to Mao Wang et al describes a method whichdecodes a received signal according to a plurality of rates, calculatesdetection statistic according to several parameters, such as CRC, symbolerror rate and the output quality value of the Viterbi decoder andselects a rate accordingly.

U.S. Pat. No. 5,638,408 to Takaki describes a method which decodes areceived signal according to a plurality of rates, compares the fourpath metric values and selects a rate accordingly.

U.S. Pat. No. 5,509,020 to Iwakiri et al describes a method whichdecodes a received signal according to a plurality of rates, comparesthe path metric of the decoder at each rate and selects a rateaccordingly.

It will be appreciated by those skilled in the art that decoding areceived encoded signal according to all possible rates requires aconsiderable amount of processing power, thereby increasing powerconsumption. This is extremely crucial in mobile communication systemssuch as cellular telephones, since these systems have limited powersources.

IS-95 communication standard (CDMA) provides two sets of communicationrates. Rate set 1, which includes 1200, 2400, 4800 and 9600 bits persecond and rate set 2, which includes 1800, 3600, 7200 and 14400 bitsper second.

Each CDMA information frame can be transmitted at any rate in a givenrate set. The present example relates to rate set 1. It will beappreciated by those skilled in the art that an IS-95 frame does notinclude any specific information indicating the rate, according to whichit was transmitted.

A receiver receiving this frame has to estimate the correct rate fromthe received data incorporated therein, in order to correctly decode theinformation bits, of that frame. According to the standard, theinformation bits are encoded in a convolutional encoder, having a rateof 1/2. Then, they are subjected to symbol repetition, depending on therate.

                  TABLE 1                                                         ______________________________________                                        Rate name           1/8    1/4    1/2   1                                     ______________________________________                                                                                  1200 2400 4800 9600                    - information bits 16 40 80 172                                              CRC bits 0 0 8 12                                                             encoder tail bits 8 8 8 8                                                      -                                                                                                                    24 48 96 192                           - repetitions (rpt) 8 4 2 1                                                  transmitted symbols N.sub.s 384 384 384 384                                 ______________________________________                                    

As will be appreciated by those skilled in the art, the number oftransmitted symbols N_(s) in each frame is three hundred and eightyfour. This number is independent of the rate used for transmitting thisframe.

The symbols are arranged in an interleaved format and multiplied firstby the user's unique Walsh function, and then by a complex pseudo random(PN) chip sequence. Each symbol is multiplied by sixth four chips, eachhaving a real component I_(c) and an imaginary component Q_(c), whereinI_(c) and Q_(c) are independent. A complex combination of the realcomponent I_(c) and the imaginary component Q_(c), given by I_(c)+jQ_(c), represents each chip. The complex output signal, which is aresult of the multiplication, is then QPSK modulated and transmitted tothe channel.

It will be appreciated by those skilled in the art that although theabove method provides reasonable rate detection results, the methodincludes a tremendous amount of calculating operations. Hence, animplementation of this method in software requires high speed processingcapabilities, which results in an increased power consumption. Animplementation of this method in hardware requires a great number ofhardware elements, which are difficult to manufacture and utilize insmall size systems.

SUMMARY OF THE PRESENT INVENTION

It is an object of the present invention to provide a novel method and anovel system for providing a rate detection which overcomes thedisadvantages of the prior art.

According to the present invention there is thus provided a ratedetection device for incorporating in a receiver, receiving an encodedsignal frame. The encoded signal frame is encoded in one of a pluralityof rates. The rate detection devices includes a plurality of encodedsignal quality estimators, each for processing the encoded signal frameaccording to a different one of the plurality of rates, therebyproducing a quality value for the rate. The device further includes acontroller, connected to the encoded signal quality estimators. Thecontroller selects the rate having the best quality value and providesthe rate to the receiver.

The rate detection device further includes a decoder connected to thecontroller for decoding the encoded signal frame according to theselected rate, thereby producing a decoded frame.

According to one aspect of the invention the device also includes anerasure detection unit, connected to the controller and the decoder,operative according to a predetermined erasure criteria, for processingthe decoded frame, thereby determining the decoded frame either asallowed or not.

In cases where the encoded frame can include CRC information, the ratedetection device further includes a decoded signal quality estimatorwhich is connected before the encoded signal quality estimators, forpre-processing the encoded signal frame according to a predetermined oneof the plurality of rates.

The decoded signal quality estimator produces a decoded quality valuefor the predetermined rate assigned thereto, decodes it and provides thedecoded frame to the receiver, when the decoded quality value exceeds apredetermined quality threshold value and there are no CRC errors. Theencoded signal quality estimators, process the encoded signal frame,otherwise. Accordingly, the decoded quality value can further include arepresentation of the presence of CRC errors in the decoded frame.

According to a further aspect of the present invention, there isprovided a rate detection device which includes at least one decodedsignal quality estimator, connected in series therebetween and furtherconnected to the host. Each decoded signal quality estimator decodes theencoded signal frame at a different rate selected from one of therate-sets available in the communication standard.

Each decoded signal quality estimator processes the encoded signal framewhen the previous one of the decoded signal quality estimators failed todecode the encoded signal frame. Each of the decoded signal qualityestimator produces a respective decoded signal quality value.

The device further includes a plurality of encoded signal qualityestimators, connected in parallel therebetween and after the decodedsignal quality estimators, for processing the encoded signal frame, eachat a different rate of the rate-set, thereby producing encoded signalquality values, only after all of the decoded signal quality estimatorsfailed to correctly decode the encoded signal frame.

The rate detection device of the invention further includes a controllerconnected to the at least one encoded signal quality estimator, adecoder connected to the controller, an erasure detection unit connectedto the controller, the decoder and the host. The erasure detection unitoperates according to a predetermined erasure criteria.

The controller selects the best of the encoded signal quality values,the decoder decodes the encoded signal frame according to the rateassociated with the selected encoded signal quality value, therebyproducing a decoded frame. Then, the erasure detection unit provides thedecoded frame to the host when determining the decoded frame allowed.

If the erasure detection unit does not allow the frame according to theselected rate, then, the controller selects the next best encoded signalquality value and the device repeats decoding and erasure detectingaccording to the current rate. This process of selecting the next bestrate can be repeated until all of the frame is analyzed according to allof the hypothesis rates.

The erasure detection unit determines the decoded frame as erased afterthe controller completed repeating the above selecting, a predeterminednumber of times.

According to yet another aspect of the invention, the rate detectiondevice of the invention further includes a plurality of decoders,connected in series therebetween and further connected to the host, eachfor decoding the encoded signal frame at a different rate selected froma second one of the rate-sets, available in the communication standard.Each decoder processes the encoded signal frame when the previousdecoder in the sequence failed to correctly decoded the encoded signalframe.

The device further includes a rate-set switch connected to the host andbefore the first of the decoded signal quality estimators and the firstone of the decoders. The rate-set switch routes the encoded signal frameaccording to the first decoded signal quality estimator, when in a modeaccording to the first rate-set and to the first decoder, when in a modeaccording to the second rate-set.

According to this aspect, a decoder of the plurality of decoders whichsucceeds in producing a correctly decoded frame, provides it to thehost.

The successes and failure of each the decoders, to decode the encodedsignal frame can determined according to an erasure detection criteria.

According to yet a further embodiment of the present invention, adaptedfor communication standards which provide provides a plurality ofrate-sets, there is thus provided a rate detection device which includesa plurality of decoders, connected in series therebetween and furtherconnected to a host, each for decoding the encoded signal frame at adifferent rate selected from a first one of the rate-sets.

Each encoder analyzes the encoded signal frame when the previous decoderfailed to correctly decode the encoded signal frame. The decoder whichsucceeds in producing a correctly decoded frame, provides the correctlydecoded frame to the host.

Each of the above encoded signal quality estimators can processes theencoded signal frame according to an encoded quality criteria which isselected from the group consisting of: ##EQU1##

The erasure criteria is selected from the group, consisting of CRCinformation, symbol error rate and accumulated Viterbi metric.

In accordance with a further aspect of the present invention, there isthus provided a method for a method for detecting the rate. The methodincludes the steps of:

processing an encoded signal according to at least two rates, in a givenrate-set, thereby producing an encoded signal quality value for each ofthe rates,

selecting the best of the encoded signal quality values,

selecting the rate associated with the selected encoded signal qualityvalue.

decoding the encoded frame according to the selected rate,

processing the decoded frame according to a predetermined erasurecriteria, thereby determining the decoded frame either as allowed or asrejected,

selecting the next best of the encoded signal quality values, whenrejecting the decoded frame (in IS-95 determining a frame as erased),

selecting the rate associated with the selected next best encoded signalquality value, and

repeating from the step of decoding the encoded frame according to theselected rate.

When the standard defines the some rates of at least one of therate-sets, as including CRC information, the method includes the stepsof:

processing the encoded frame at a elected rate of the plurality of theserates, thereby producing a decoded signal rate quality value,

repeating the step of processing for another elected one of these rates,when failing to correctly decode the encoded frame or when the qualityvalue does not exceed a predetermined threshold value.

For the rates which do not include CRC information as well as for framesof CRC associated rates, which may further be used even if includingsome errors, the method further includes the steps of:

processing the encoded signal according to a plurality of rates, therebyproducing an encoded signal quality value for each of the rates, whenfailing to correctly decode the encoded frame at selected rates of theabove CRC associated rates,

selecting the best of the encoded signal quality value, and

selecting the rate associated with the selected encoded signal qualityvalue.

decoding the encoded frame according to the selected rate, and

processing the decoded frame according to a predetermined erasurecriteria, thereby determining the decoded frame either as allowed or asrejected.

Accordingly, similar to the previous method, the process can be repeatedfor the next best of the encoded signal quality values, when rejectingthe decoded frame, according to the current selected value.

The present invention undertakes a further novel approach to ratedetection, where it utilizes the user data power of a received frame inthe process of detecting the correct rate.

The encoded signal quality value, used in the above methods of theinvention is calculated, for example, according to a quality criteria,selected from the group consisting of: ##EQU2##

Some communication standards, define the user data power to bedifferent, at different rates. Accordingly, when comparing the user datapower of a received frame with respect to other types of data in thatframe as well as to user data power detected for previously receivedframes, one can determine the rate of the received frame, therefrom.

Accordingly, in accordance with another aspect of the invention, thereis provided a method which includes the steps of:

analyzing the received encoded frame at a plurality of rates, therebyproducing a user data power associated quality values therefrom,

selecting the best of the user data power associated quality value, and

selecting the rate associated with the selected user data powerassociated quality value.

The step of analyzing can further include comparing the user data powerof the encoded frame with user data power of previous analyzed frames,as well as with respect to the rate determined for the previous analyzedframe.

The method can further include the steps of:

decoding the encoded frame according to the selected rate,

processing the decoded frame according to a predetermined erasurecriteria, thereby determining the decoded frame either as allowed or asrejected,

selecting the next best of the encoded signal quality values, whenrejecting the decoded frame,

selecting the rate associated with the selected next best encoded signalquality value, and

repeating from the step of decoding the encoded frame according to theselected rate.

The failing to correctly decode the encoded frame is determinedaccording to an erasure criteria, which can be selected from the group,consisting of:

CRC information;

symbol error rate; and

accumulated Viterbi metric.

The encoded signal quality value, used in the above methods of theinvention is calculated, for example, according to a quality criteria,selected from the group consisting of: ##EQU3##

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description taken in conjunction with thedrawings in which:

FIG. 1 is a schematic illustrating of a rate detection system, known inthe art;

FIGS. 2A and 2B which are schematic illustrations of the power ofuser-data signal in CDMA frames;

FIG. 3 is a schematic illustration of transition chart between aplurality of frame states;

FIG. 4 is a schematic illustration of a method for detecting theencoding rate of a received frame using user data power, operative inaccordance with a preferred embodiment of the present invention;

FIG. 5 is a schematic illustrating of a rate detection system,constructed and operative according to another preferred embodiment ofthe present invention;

FIG. 6 is a schematic illustration of a method for operating the systemof FIG. 5, operative in accordance with a further preferred embodimentof the present invention;

FIG. 7 is a schematic illustration of a rate detecting system,constructed and operative in accordance with another preferredembodiment of the invention;

FIG. 8 is a schematic illustration of a method for operating the systemof FIG. 7, operative in accordance with yet another preferred embodimentof the present invention;

FIG. 9 is a schematic illustration of a system for detecting rate,constructed and operative in accordance with another preferredembodiment of the present invention;

FIG. 10 is a schematic illustration of a method for operating the systemof FIG. 9, operative in accordance with a further preferred embodimentof the present invention;

FIG. 11 is a schematic illustration of a system for detecting rate,constructed and operative in accordance with another preferredembodiment of the present invention; and

FIG. 12 is a schematic illustration of a method for operating the systemof FIG. 11, operative in accordance with a further preferred embodimentof the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The method of the present invention overcomes the disadvantages of theprior art, by providing a encoded signal likelihood estimating mechanismwhich reduces and often eliminates the need to decode a signal beforeattempting to detect its rate.

The method of the present invention provides several simplified rate anderasure decision criteria. The method of the present invention alsoprovides an erasure criterion, which is based on CRC information and onsymbol error rate or on accumulated Viterbi metric, or on a combinationof the above.

The definition of the basic terms used hereinbelow can be found in"CDMA--principles of spread spectrum communication", by A. J. Viterbi(publ--Addision-Wesley Publishing Company 1995.

i is the index of a transmitted symbol,

j is the index of a transmitted chip within that symbol,

n is the index of a user, and

t is a time variable.

Accordingly, walsh,(j) is the value of the Walsh function (a moreprecise notation is walsh_(n) (j); for simplicity the n subscript isomitted),

pn(64·i+j) is the complex PN chip,

sym(i) is the symbol transmitted (more precisely, sym_(n) (i)), and

s(·) is the pulse shaping signal.

Hence, tx(t,i,j) (more precisely, tx_(n) (t,i,j)), the contribution ofthe j-th chip of the i-th symbol, transmitted to the n-th user, to thetransmitted base-band signal, is given by,

    tx(t,i,j)=c·sym(i)·walsh(j)·pn(64·i+j).multidot.s(t-(64·i+j)T.sub.c)

where T_(c) is the chip duration.

Similarly, the corresponding contribution to the base-band pilot signal,is given by

    tx.sub.0 (t,i,j)=pn(64·i+j)·s(t-(64 ·i+j)T.sub.c)

where c is the ratio of the user-data signal amplitude to the pilotsignal amplitude. Hence, for each finger f, the contribution of the j-thchip of the transmitted i-th symbol to the received user and pilotbase-band signals, r(t,f,i,j), and r_(o) (t,f,i,j) are given by

    r(t,f,i,j)=tx(t,i,j)·Ae.sup.jφ

    r.sub.0 (t,f,i,j)=tx.sub.0 (t,i,j)·Ae.sup.jφ

wherein A is the amplitude of the finger and φ is the phase. This methodassumes that any additional delay in the finger is known, and hence, canbe neglected.

At the receiver end, the user and pilot signals are first processed bythe matched filter, and then sampled appropriately. Then, the receiverde-interleaves the resulting samples, multiplies both by the conjugateof the PN sequence and then, multiplies the user signal also by itsWalsh chip sequence. Finally, the receiver integrates by way ofsummation, the chips of the symbol. The resulting signals, d(f,i) and d₀(f,i) are given by, ##EQU4## wherein * denotes a complex conjugateoperator, r^(M) (t,f,i,j) and r₀ ^(M) (t,f,i,j) denote the sampled userand pilot matched filter outputs and A₁ =128 A·n(f,i) is an additivenoise term (contributed by signals transmitted to other users by thesame transmitter, other transmitters and also by channel noise) which isdependent of the finger f.

The method assumes that the variance σ² of n(f,i) is independent of thefinger f. It is noted that d₀ (f,i) does not include an additive noiseterm due to channel tracking (smoothing) operation that is assumedpresent.

Based on the given measurement data, d(f,i) and d₀ (f,i), of the currentframe, the receiver detects the encoded information bits. The ratedecision problem is how to make a reliable detection of the rate,according to which the information bits were encoded.

The erasure detection problem is how to make a reliable decision whetherthe decoded information bits are free of errors. The method of theinvention determines a frame as erased, when the output metric of theViterbi decoder exceeds a predetermined value or when the frame includesmore than a predetermined number of errors, or a combination of theabove.

According to one aspect of the present invention there is provided amethod for estimating a bit sequence, which is operative under theassumption that the transmission rate is unknown.

Further to the definitions made hereinabove,

N_(f) is the number of fingers,

bits is the bit sequence encoded at the convolutional encoder of then-th user, which corresponds to a hypothesis of a selected rate,

l(data) is the log likelihood of the data, and

l(data|syms) is the a-posterior log- likelihood given an hypothesizedsymbol sequence syms.

rpt is the symbol repetition factor, i.e.

    sym(rpt·(j-1)=sym(rpt·(j-1)+2)= . . . =sym(rpt·j)

(for rotational simplicity we assume that de-interleaving has alreadybeen applied on the receiver symbols).

According to another aspect of the present invention, there are providedseveral signal rate decision criteria, which determine the rate based onl(data), under the assumption that coding is not present. These criteriaare based on the following derivation: ##EQU5## where ##EQU6## Thelikelihood of the symbol sequence syms is: ##EQU7## Hence, ##EQU8##

The summation over syms denotes a summation over all symbol sequences.Using some straight-forward algebraic manipulations the followingexpression is obtained, ##EQU9##

The second term -N_(s) log2/rpt on the right hand side (RHS) tends toincrease as rpt increases, while the third term on the RHS ##EQU10##monotonically decreases as rpt increases.

To avoid underflows, the last term on the right-hand side of theequation is calculated using, ##EQU11##

It will be noted that both c and σ should be estimated from the givendata. To estimate c and σ the method provides a ML estimation procedurefor the case where neither coding nor repetition are exploited. In thiscase the likelihood of the data given the symbols is given by ##EQU12##

Hence, the ML estimate of sym(i), which is denoted by sym(i) is given by##EQU13## (since c>0). Hence, ##EQU14##

The ML estimate of c(c) is obtained by optimizing Equation 4 withrespect to c (i.e., setting the respective derivative to 0), and byinvoking Equation 5. Using straight-forward algebraic manipulations weobtain, ##EQU15##

Similarly, σ, which is the ML estimated value of σ, is obtained byoptimizing Equation 4 with respect to σ (i.e., setting the respectivederivative to 0). Accordingly, ##EQU16##

According to a further aspect of the present invention there areprovided generalized signal rate detection criteria, using Equation 3(note that K is independent of the rate, since the estimates of c and σare independent of the rate. Hence, K may be ignored, i.e. it may be setto 0) to determine the rate.

For example, l(data) can be calculated according to either of thefollowing expressions: ##EQU17## where β is a parameter of the method.

c_(rate) is generally a constant which is dependent on the rate, forexample:

    c.sub.rate =-N.sub.s log 2/rpt.

Accordingly, ##EQU18##

According to a further aspect of the present invention, there isprovided a method for smoothing σ, which is the ML estimated value of σ,given in Equation 7, by calculating an average value across the currentand previous frames. For example:

    σ.sub.t.sup.2 =σ.sub.t-1.sup.2 ·δ+σ.sub.t.sup.2 ·(1-δ)Equation 12

wherein 0≦δ<1

To develop the following methods, we invoke an approximation, log(e^(x)+e^(-x))≅|x| in Equation 3 to obtain, ##EQU19## where K is given byEquation 2. Optimizing Equation 13 with respect to c and σ (i.e.,setting the respective derivatives to 0), yields, ##EQU20##

Substituting Equation 14 back into Equation 13 yields (up to a constantadditive term) ##EQU21##

According to another aspect of the invention, Equation 14 and Equation15 are used to determine the rate. In order to enable more flexibilitythe present invention provides the following expression:

    l(data)=-γN.sub.s N.sub.f log (E.sub.u -c.sup.2 E.sub.p)+c.sub.rate.Equation 16

c_(rate) is a constant which is dependent on the rate, for example,##EQU22## Hence, ##EQU23## where β is a parameter of the method.

Note that according to another aspect of the invention, l(data) can becomputed using Equation 16. Then, the resulting value is corrected byadding a correction term, ##EQU24## which is the difference betweenEquation 3 and Equation 13.

According to another aspect of the invention, the rate can be evaluatedby incorporating user-data power information. According to CDMA standardIS-95, the rate assigned to a particular frame, determines the amplitudeof the user-data in that frame.

Whenever the rate increases, user-data power increases by the sameamount, so as to keep the energy of a transmitted information bitconstant. The power of the pilot signal does not change as the ratechanges.

Hence, the present invention provides a method in which the power of theuser-data in each frame is incorporated in the rate detection criteria,so as to determine the rate of that frame.

Reference is now made to FIGS. 2A and 2B which are schematicillustrations of the power of user-data signal in CDMA frames.

In FIG. 2A, bars 400, 402, 404 and 406, represent the power of theuser-data in 1/8, 1/4, 1/2 and full rate frames, respectively. The power406 of a full rate frame is twice the power 404 of the user-data of ahalf rate frame, four times the power 402 of the user-data of a 1/4 rateframe and eight times the power 400 of the user-data of a 1/8 rateframe.

According to one aspect of the invention, the user-data power of eachframe is scaled according to the user-data power of the previous frame.Referring now to FIG. 2B, the transition from an 1/8 rate frame 410 to a1/2 rate frame 412 yields in a ×4 power ratio (i.e., ##EQU25## whereinc₁ is the power of a selected frame and c₂ is the power of the nextframe.

Accordingly, the transition from frame 412 to frame 414 yields a ×2power ratio, the transition from frame 414 to frame 416 yields a :4power ratio, the transition from frame 416 to frame 418 yields a ×4power ratio and the transition from frame 418 to frame 420 yields a :8power ratio.

It will be appreciated that if A₁ and P₁ are the amplitude and power ofa first frame, respectively and A₂ and P₂ are the amplitude and power ofa second frame, respectively, then, ##EQU26## Accordingly, a powertransition of ×2 would result in an amplitude transition of x√2.

Reference is now made to FIG. 3, which is a schematic illustration oftransition chart between a plurality of frame states.

States 500, 502, 504 and 506, respectively represent a full, half,quarter and eighth rate states of a first frame. States 510, 512, 514and 516, respectively represent a full, half, quarter and eighth ratestates of a second frame. States 520, 522, 524 and 526, respectivelyrepresent a full, half, quarter and eighth rate states of a third frame.

Each of the arrows connecting between two states, represents a potentialrate transition. Transition 530 represents a rate transition betweenstate 500 and state 510. Transition 542 represents a rate transitionbetween state 510 and state 522.

According to the present invention, if the user-data power of the secondframe is four times greater than the user-data power of the first framethen the rate transitions which apply are 538 and 539. Accordingly, thepresent invention eliminated fourteen transitions.

According to another example, if the user-data power of the second frameis a division by two of the user-data power of the first frame then, therate transitions which apply are 532, 572 and 574. Accordingly, thepresent invention eliminated thirteen transitions.

According to a further example, if the user-data power of the secondframe is equal to the user-data power of the first frame than the ratetransitions which apply are 530, 576, 578 and 580. Accordingly, thepresent invention eliminated twelve transitions. It will be noted thatwhen the rate of the first frame is known then, the rate of the secondframe can be precisely obtained from the user-data power measurements.

According to another aspect of the present invention, the transitiontrail is extended to more than two frames. For example, if the user-datapower of the second frame is four times greater than the user-data powerof the first frame and the user-data power of the third frame is greaterthan the user-data power of the second frame by a factor of two, then,the rate transition trail which applies includes transitions 538 and560.

In accordance with another aspect of the invention, there is thusprovided a rate detection criteria which incorporates user-data power.

Let c₁ and c₂ be the ratio of the user-data signal amplitude to thepilot signal amplitude in the previous and current frames, respectively,and let γ=c₂ /c₁. Let the data measurements at the previous and currentframes be denoted by data₁ and data₂, respectively. The likelihood ofthe data measurements in the previous and current frames (given therates) is ##EQU27## where rpt₁ and rpt₂ are the repetition factors inthe previous and current frames. Note that γ=√rpt₁ /rpt₂ . In addition,##EQU28## where E_(u).sbsb.1, E_(u).sbsb.2 are the user-data energies inthe previous and current frames. E_(p).sbsb.1 and E_(p).sbsb.2 are thepilot energies in the previous and current frames.

Equation 18 may be simplified by invoking the approximation log(e^(x)+e^(-x))≅|x|, yielding ##EQU29##

Given the rates of the previous and current frames, and hence γ, c₁ andσ are obtained by optimizing Equation 19 with respect to c₁ and σ (i.e.setting the appropriate derivatives to 0). This yields, ##EQU30##

Substituting Equation 20 and Equation 21 back into Equation 19 yields,##EQU31##

To enable more flexibility, the suggested method is ##EQU32## where forexample ##EQU33##

Equation 23 may be improved by adding a correction term such as:##EQU34## wherein c₂ =γ·c₁

A simple rate decision method may be implemented by calculatingl(data₁,data₂) for each pair of consecutive frames, for all 16possibilities of current and previous rates. The estimated current rateis the rate for which the maximal value of l(data₁,data₂) is obtained.

We now present an improved rate decision method that is based on dynamicprogramming. Let l_(ij) (data₁,data₂) denote the likelihood of theprevious and current frames under the assumption that the rate at theprevious frame is i, and the rate at the current frame is j. a_(j)represents a current accumulated likelihood variable, under theassumption that the current rate is j. Similarly, a_(i) represents aprevious accumulated likelihood variable, under the assumption that theprevious rate is i. a_(j) is computed using ##EQU35##

where ρ is some forgetting factor (e.g. 0.7). The estimated current rateis ##EQU36##

Reference is now made to FIG. 4 which is a schematic illustration of amethod for detecting the encoding rate of a received frame using userdata power, operative in accordance with yet another preferredembodiment of the present invention. The method includes the followingsteps:

A. Receiving a frame of encoded signal (step 700),

B. Detecting user data power information, which is included in thereceived frame (step 702);

C. Processing the user power information of the current received framewith respect to previous frames (step 704). In this step, the methodproduces a quality value for each rate and rate transition, which isused later to detect the correct rate, according to which the receivedframe was encoded.

D. Selecting the rate having the best quality value (step 705). Themethod of the present invention further includes additional steps whichprovide enhanced performance, refining the detection of the correctrate.

E. decoding the received encoded frame according to the selected rate(706).

F. Detecting if the frame should be erased (step 708). It will be notedthat any erasure criteria, which is known in the art, is applicable forthe present invention.

G. Determining the selected rate as the rate of the encoded receivedframe, when the frame qualifies the erasure detection (step 710).

H. Selecting the rate with the next best quality value, when the framedid not qualify the erasure detection (step 712) and repeating from step706 for this rate.

It will be noted that the repeating of steps 706 through 712 can belimited for a predetermined number of repetitions, a predetermined limitvalue for the quality values, and the like.

It will be further noted that the user data power information can beused directly, as described hereinabove, or indirectly, incorporated inencoded signal rate quality value criteria as described in Equation 18,Equation 19, Equation 20, Equation 21, Equation 22, Equation 23,Equation 24 and Equation 25.

Reference is now made to FIG. 5, which is a schematic illustration of arate detection system, generally referenced 100, constructed andoperative in accordance with a preferred embodiment of the presentinvention.

System 100 includes a plurality of encoded signal quality estimatingunits 102, 104, 106 and 108, a decision controller 110, connected tounits 102, 104, 106 and 108 and a decoder 112, connected to the decisioncontroller.

The estimating unit 102, 104, 106 and 108 can be implemented in hardwareor software. Each of these estimating units, detects the received signaland processes, according to a quality criteria set forth by the presentinvention, with respect to a different rate, thereby yielding a qualityvalue.

The quality value can be calculated using either Equation 8, with orwithout the smoothing expression provided in Equation 12, Equation 9,with or without the smoothing expression provided in Equation 12,Equation 16, Equation 16 with the correcting term of Equation 17,Equation 23, Equation 23 with the correcting term of Equation 24 orEquation 25.

The received encoded signal is provided to each of the encoded signalquality estimating units 102, 104, 106 and 108 which, in turn, processesthe encoded signal, each according to a predetermined rate. Estimatingunits 102, 104, 106 and 108 processed the encoded signal according torate=1, 1/2, 1/4 and 1/8, respectively and produce a quality valueaccordingly.

Then, the decision controller 110 detects the best quality value,thereby selecting the rate which is most likely for the received signalframe. Finally, the decision controller 110 provides a specific ratedecoding command to decoder 112, which in turn decodes the receivedsignal according to the selected rate.

By eliminating the need to decode the encoded frame at all of thepossible rates, system 100 reduces the amount of resources and powerrequired for detecting the correct rate.

Reference is now made to FIG. 6 which is a schematic illustration of amethod for operating system 100, operative in accordance with anotherpreferred embodiment of the present invention.

In step 150, the system receives an encoded signal.

In step 152, the system analyzes the encoded signal at different rates,according to one of the above quality criterion. Then, the systemproduces a quality value Q(i) for each of the rates i (step 154).

In step 156, the system selects the rate which has the best qualityvalue Q(i). It will be noted that, according to the present embodiment,the system reaches a decision for the appropriate rate without decodingthe encoded signal at all.

Finally, after determining the appropriate rate, the system decodes theencoded signal according to the selected rate (step 158) and provides adecoded signal as output for further processing.

Reference is now made to FIG. 7 which is a schematic illustration of arate detecting system, generally referenced 300, constructed andoperative in accordance with yet a further preferred embodiment of theinvention.

System 300 includes a plurality of encoded signal quality estimatingunit 302, 304, 306 and 308, a decision controller 310 connected to units302, 304, 306 and 308, a decoder 312, connected to the decisioncontroller 310 and an erasure detection unit 314 connected to thedecoder 312.

Each of the encoded signal quality estimating units 302, 304, 306 and308 analyses the encoded signal frame according to a different rate,processes it according to an encoded quality criterion as describedabove, produces an encoded quality value Q(i) for each of the hypothesisrates, using either and provides this quality value to the decisioncontroller 310.

The quality value Q(i) can be calculated using either Equation 8, withor without the smoothing expression provided in Equation 12, Equation 9,with or without the smoothing expression provided in Equation 12,Equation 16, Equation 16 with the correcting term of Equation 17,Equation 23, Equation 23 with the correcting term of Equation 24 orEquation 25.

The decision controller 310 sorts the received encoded likelihood valuesQ(i), determines the rate with the best encoded likelihood value Q(i)and provides it to the decoder 312. The decoder 312 decodes the encodedsignal frame, according to this rate, thereby producing a decoded signalframe and provides it to the erasure detection unit 314.

The erasure detection unit 314 analyses the decoded signal frame so asto determine if this frame is to be allowed or erased. If this frame isto be allowed then the erasure detection unit 314 provides it to thetransceiver apparatus for further processing according to the selectedrate. Otherwise, the erasure detection units 314 informs the decisioncontroller that this frame is not allowed.

The erasure detection unit 314 operates according to an erasuredetection criteria which is based on CRC information, bit error rateestimation or accumulated Viterbi metric. It will be noted that theerasure criteria can also be based on a combination of CRC information,bit error rate estimation and accumulated Viterbi metric.

The decision controller 310 then selects the rate with the next bestencoded quality value Q(i) and provides it to the decoder 312. Then, thedecoder 312 decodes the encoded signal frame according to this rate,thereby producing a decoded frame and provides it to the erasuredetection unit 314.

The erasure detection unit 314 analyses the frame, according to the nextbest encoded likelihood value, and determines if this frame is to beerased or allowed. If the erasure detection unit 314 determines thatthis frame is to be allowed, then it provides it to the transceiverapparatus for further processing according to this rate. Otherwise, theerasure detection unit 314 instructs the rest of the system 300 toproceed to the next encoded signal frame (i.e., the current frame is tobe erased).

It will be noted that the operation of repeating decoded and detectingerasure can be performed either for all of the rates, as long as thesignal frame fails the erasure test, or end at a predetermined number ofquality level (i.e., for example stop after the next best quality valueand proceed to the next frame).

Reference is now made to FIG. 8 which is a schematic illustration of amethod for operating system 300, operative in accordance with yetanother preferred embodiment of the present invention.

In step 350, the system 300 receives a frame of encoded signal.

In step 352, the system 300 analyses the encoded signal at differentrates I, produces an encoded quality value Q(i) for each of the rates i(step 354).

In step 356, the system selects the rate with the best encoded qualityvalue Q(i).

In step 358, the system decodes the encode signal frame according to theselected rates, having the best encoded quality value Q(i).

In step 360, the system 300 determines if the decoded frame is to beeither allowed or erased. If the frame is to be allowed, then this frameshould be further processed according to this rate. Otherwise, thesystem 300 proceeds to step 364.

In step 364, the system selects the rate with the next best encodedquality value Q(i).

In step 366, the system 300 decodes the encoded signal according to thecurrent selected rate, having the next best encoded likelihood value.

In step 368, the system determines if this frame is to be either allowedor erased. If the system 300 determines that this frame is to beallowed, then it provides the frame, together with the current selectedrate, to a transceiver apparatus, in which system 300 is incorporated,for further processing according to this rate (step 372). Otherwise, thesystem rejects (erases) this frame and proceeds to the next frame (step370).

It will be noted that steps 364, 366, 364, 370 and 372, can beduplicated for further levels of detection, for example, for the thirdbest quality value, and the like.

It will be appreciated that the present invention provides severalapproaches to determine the rate of a received frame without decodingand re-encoding the frame according to all of the possible ratehypotheses. It will be noted that each of these novel and innovativeapproaches can be combined to produce an enhanced rate detectionmechanism.

Reference is now made to FIG. 9, which is a schematic illustration of asystem for detecting rate, generally referenced 200, constructed andoperative in accordance with another preferred embodiment of the presentinvention.

System 200 includes a decoded signal quality estimator 202 for rate9600, an encoded signal quality estimator 204, for rate 9600, encodedsignal quality estimators 206, 208 and 210 for rates 4800, 2400 and1200, respectively, a controller 212, a decoder 214 and an erasuredetection unit 216.

Encoded signal quality estimators 204, 206, 208 and 210 are connected tocontroller 212 and to decoded signal quality estimator 202. Controller212 is further connected to decoder 214 and to erasure detection unit216, which are further connected therebetween. The erasure detectionunit 216 is also connected to a host 220.

Decoded signal rate quality estimator 202 receives an incoming encodedsignal frame, decodes it at a rate of 9600 and calculates quality valueswhich incorporates CRC information, bit error rate and accumulatedViterbi metric or a combination of the above.

If the quality values exceed predetermined threshold values and thedecoding process is complete without any CRC errors, then, the decodedsignal rate quality estimator 202 provides the decoded signal to thehost 220 and proceeds to the next frame. Otherwise, the decoded signalrate quality estimator 202 provides the encoded frame to encoded signalestimators 204, 206, 208 and 210.

The encoded signal estimators 204, 206, 208 and 210, process the encodedsignal, thereby producing quality value, each for its predetermined rateand provide these values to the controller 212. The controller 212selects the rate with the best quality value and provides it with theencoded frame to the decoder 214. The decoder 214 decodes the encodedframe and provides it to the erasure detection unit 216, which in turnprocesses it according to an erasure criteria as set forth hereinabove.

If the erasure detection unit 216 determines that the frame is to beallowed, then it provides the decoded frame to the host 220. Otherwise,the erasure detection unit 216 instructs the controller 212 to proceedto the rate with the next best quality value and the process of decodingand erasure detecting is repeated for this rate.

By eliminating the need to decode the encoded frame at all of thepossible rates, system 200 reduces the amount of resources and powerrequired for detecting the correct rate.

Reference is now made to FIG. 10 which is a schematic illustration of amethod for operating the system of FIG. 9, operative in accordance witha further preferred embodiment of the present invention.

In step 250, the system 200 (FIG. 9) receives a frame of encoded signal.The system 200 processes the frame according to a hypothesis ofrate=9600, thereby decoding it and producing a quality value therefore(step 252.

In step 254, the system 200 detects if the quality of value exceeds apredetermined threshold and that the decoding of this frame according torate=9600 is completely without CRC errors. If so, then the system 200proceeds to step 258 where it provides the decoded frame to a host,connected thereto. Otherwise, the system 200 proceeds to step 256.

In step 256, the system 200 produces an encoded signal rate qualityvalue for each of the rates in the rate-set. It will be noted that theencoded quality value for rate=9600 determines if this frame, whenpredetermined as a speech frame, although probably included CRC errors,may still be used. If will further be noted that this is not possiblefor a data frame.

In step 260, the system 200, detects best quality value (be itmaximized, minimized, and the like), selects the rate, associatedtherewith and decodes the received frame according the selected rate(step 262).

In step 264, the system 200 processes the decoded according to anerasure criteria. If the system 200 determines the frame as erased,then, the system 200 selects the rate with the next best quality valueand repeats from step 262. Otherwise, the system proceeds to step 258.

In step 258, the system 200 provides the decoded frame to a host,connected thereto.

Reference is made now to FIG. 11, which is a schematic illustration of asystem for detecting rate, generally referenced 600, constructed andoperative in accordance with another preferred embodiment of the presentinvention.

System 600 includes a rate-set switch 620, a plurality of rateestimators 602, 604, 606, 608 and 610, a plurality of decoders 612, 614,616 and 618, a controller 622, a decoder 626 and an erasure detectionunit 624. System 600 is connected to a host 630.

System 600 is adaptive to operate at two rate-sets, providing aspecialized section for each of them. The section operative according torate-set one includes rate estimators 602, 604, 606, 608 and 610. Thesection operative according to rate-set two includes decoders 612, 614,616 and 618.

Rate-set switch 620 is connected to the host 630, rate estimator 602,decoder 612 and to an encoded signal source (not shown). Decoded signalrate quality estimator 602 is further connected to the host 630 and todecoded signal rate quality estimator 604. Decoded signal rate qualityestimator 604 is further connected to encoded signal rate qualityestimators 606, 608 and 610 as well as to the host 630. encoded signalrate quality estimators 606, 608 and 610 are further connected to thecontroller 622.

Decoder 612 is further connected to decoder 614 and to the host 630.Decoder 614 is further connected to decoder 616 and to the host 630.Decoder 616 is further connected to decoder 618 and to the host 630.Decoder 618 is further connected to the host 630.

The decoder 626 and the erasure detection unit 624 are connectedtherebetween, as well as to the controller 622. The erasure detectionunit 624 is further connected to the host 630.

The host 630 provides a rate-set mode command to the rate-set switch620, for operating the system 600 according to one of the rate sets,rate-set one or rate-set 520. The rate-set switch 620 receives anencoded signal frame and provides it to decoded signal rate qualityestimator 602, when operating in rate-set one mode and to decoder 612,when operating in rate-set two mode.

Decoded signal rate quality estimator 602 decodes the encoded signalframe according to rate=9600 and produces a quality value, associatedtherewith. If the quality value exceeds a predetermined value and theframe is decoded with no CRC errors, then the decoded signal ratequality estimator 602 provides the decoded frame to the host 630.Otherwise, the decoded signal rate quality estimator 602 provides theencoded frame to decoded signal rate quality estimator 604.

Decoded signal rate quality estimator 604 decodes the encoded signalframe according to rate=4800 and produces a quality value, associatedtherewith. If the quality value exceeds a predetermined value and theframe is decoded with no CRC errors, then the decoded signal ratequality estimator 604 provides the decoded frame to the host 630.Otherwise, the decoded signal rate quality estimator 604 provides theencoded frame to encoded signal rate quality estimators 606, 608 and610.

Encoded signal rate quality estimators 606, 608 and 610 process theencoded frame according to rates of 9600, 2400 and 1200, respectively,thereby producing respective quality values and provide them to thecontroller 622. The controller 622 selects the best quality value andprovides the encoded signal to decoder 626, along with a command todecode it according to the rate associated with the selected rate.

The decoder 626 produces a decoded frame and provides it to the erasuredetection unit 624, which in turn determines if the frame should beallowed or erased. If the erasure detection unit 624 determines that theframe is to be allowed, it provides it to the host 630. Otherwise, theerasure detection unit 624 informs the controller 622 that the frame, asencoded according to the selected rate, is not allowed.

Then, the controller 622 selects the next best quality value andprovides a command to the decoder 626, so as to decode the encoded frameaccording to the rate associated therewith. The process of decoding theframe and detection erasure is then repeated for this rate andoptionally for the third rate unit the frame, decoded according to oneof the rates is either allowed or finally rejected (erased).

Decoder signal rate quality estimator 612 decodes the encoded signalframe according to rate=14400, produces a 14400 decoded quality value,associated therewith. The 14400 decoded quality value can be calculatedaccording to either CRC information, symbol error rate, accumulatedViterbi metric or on a combination thereof.

If the 14400 decoded quality value exceeds a predetermined thresholdvalue and the respective decoded frame does not include CRC errors,then, the decoder 612 provides the decoded frame to the host 630.Otherwise, the decoder 612 provides the encoded signal to decoder 614.

Decoder 614 repeats the same operations performed by decoder 612, forrate=7200 and produces a 7200 decoded quality value. Accordingly, if the7200 decoded quality value exceeds a predetermined threshold value andthe respective decoded frame does not include CRC errors, then, thedecoder 614 provides the respective decoded frame (now decoded accordingto rate=7200) to the host 630. Otherwise, the decoder 614 provides theencoded signal to decoder 616.

Decoder 616 repeats the same operations performed by decoder 614, forrate=3600 and produces a 3600 decoded quality value. Accordingly, if the3600 decoded quality value exceeds a predetermined threshold value andthe respective decoded frame does not include CRC errors, then, thedecoder 616 provides the decoded frame (now decoded according torate=3600) to the host 630. Otherwise, the decoder 616 provides theencoded signal to decoder 618.

Finally, decoder 618 repeats the same operations performed by decoder616, for rate=1800 and produces a 1800 decoded quality value. If the1800 decoded quality value exceeds a predetermined threshold value andthe respective decoded frame does not include CRC errors, then, thedecoder 618 provides the decoded frame (now decoded according torate=1800) to the host 630. Otherwise, the decoder 618 informs the host630 that the encoded frame failed decoding according to all of the ratesin the rate-set and as such should be erased.

By eliminating the need to detect the encoded frame at all of thepossible rates, the above cascade structure, provided for system 600,reduces the amount of resources and power required for detecting thecorrect rate.

As long as the frame is not allowed, the above process is repeated forthe next rate, serially. Finally, if the frame is erased for theserates, then the system 600 proceeds to the next received frame.

Reference is now made to FIG. 12 which is a schematic illustration of amethod for operating the system of FIG. 11, operative in accordance witha further preferred embodiment of the present invention.

In step 650, the system 600 receives a frame of encoded signal anddetermines, according to a predetermined host command the rate-set,according to which the frame is to be analyzed (step 652). If the frameis to be analyzed according to rate-set one, then, the system 600proceeds to step 654. Otherwise, the system 600 proceeds to step 680.

In step 654, the system 600 produces a decoded signal rate qualityvalue, at rate=9600.

In step 656, the system 600 determines if the decoding quality of theframe according to this rate is high enough, by detecting if the qualityvalue exceeds a predetermined threshold value and by detecting if thedecoded frame has no CRC errors. If so, then the system proceeds to step690. Otherwise, the system proceeds to steps 658 and 660, therebyrepeating the process of steps 654 and 656 according to rate 4800.

If the quality according to rate=4800 is determined high then, thesystem proceeds to step 662, thereby producing an encoded signal ratequality value for rates 9600, 2400 and 1200.

In step 664, the system 600 selects the best quality value, from theones produces in step 662 and decodes the encoded frame according to therate associated therewith (step 666).

In step 668, the system 600 determines if the decoded frame, is to beerased or allowed. If the frame is to be erased, then the system 600determines if the encoded frame is to be further analyzed according toone or two of the remaining rates (step 670). If so, then the system 600selects the rate with the next best quality value (step 672) and repeatssteps 666 and for 668 for this selected rate.

If the system 600 determines in step 668 that the frame is allowed,then, it provides the decoded frame and rate information to a hostconnected thereto (step 690).

In step 680, the system 600 selects the highest rate in rate-set two,which in the present example (IS-95) is 14400 bits per second.

In step 682 the system 600 produces a decoded signal rate quality valueat the selected rate.

In step 684, the system 600 determines if the quality of the decodingprocess according to the selected rate is high enough, by detecting ifthe quality value exceeds a predetermined threshold value and therespective decoded frame has no CRC errors. If the quality is determinedhigh, then, the system 600 proceeds to step 690, where it provided thedecoded frame and rate information to the host, connected thereto.

Otherwise, the system 600 detects if the selected rate is the lowestavailable. If not, then, the system selects the lower rate (at thisstage rate=7200, followed later by rate=3600, which in turn is followedby rate=1800--the lowest rate available) and repeats from 682.

The above quality evaluation equations are provided under the assumptionthat puncturing is not present, after symbol repetition. It will benoted that converting these equations for use in an environment whichincludes puncturing, either power control puncturing or codingpuncturing (as in rate-set 2 of IS-95) requires straight forwardalgebraic modifications.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather the scope of the present invention isdefined only by the claims which follow.

What is claimed is:
 1. In a receiver receiving an encoded signal frame,the encoded signal frame being encoded in one of a plurality rates, arate detection device comprising:a plurality of encoded signal qualityestimators each having a different one of said plurality of ratesassociated therewith, wherein each estimator processes said encodedsignal frame according to its associated rate, thereby producing aquality value for said associated rate; a decoded signal qualityestimator connected before said encoded signal quality estimators, forpre-processing and encoded signal frame according to a predetermined oneof said plurality of rates; and a controller connected to said pluralityof encoded signal quality estimators, wherein said controller selectsthe rate having the best quality value and provides said selected rateto said receiver, wherein said decoded signal quality estimator producesa decoded quality value for said predetermined rate, decodes said frameaccording to said predetermined rate and provides said decoded frame tosaid receiver when said decoded quality value exceeds a predeterminedquality threshold value, wherein said encoded signal quality estimatorsprocess and encoded signal frame when said decoded quality value doesnot exceed said predetermined quality threshold value.
 2. The ratedetection device according to claim 1 wherein said decoded quality valuefurther includes a representation of the presence of CRC errors in saiddecoded frame.
 3. In a receiver including a host, receiving an encodedsignal frame, the encoded signal frame being encoded in a particularrate in a given rate-set, the rate-set selected from a plurality ofrate-sets, each rate-set including a plurality of rates, a ratedetection device comprising:at least one decoded signal qualityestimator, connected in series therebetween and further connected tosaid host, each for decoding said encoded signal frame at a differentrate selected from a first one of said rate-sets, when the previous oneof said at least one decoded signal quality estimator failed to decodesaid encoded signal frame, and for producing a decoded signal qualityvalue thereof, a plurality of encoded signal quality estimators,connected in parallel therebetween and after said at least one decodedsignal quality estimator, for processing said encoded signal frame, eachat a different rate of said first rate-set, thereby producing encodedsignal quality values, when all of said at least one decoded signalquality estimator failed to correctly decode said encoded signal frame,a controller connected to said at least one encoded signal qualityestimator, a decoder connected to said controller, an erasure detectionunit connected to said controller, said decoder and said host, operativeaccording to a predetermined erasure criteria, wherein said controllerselects the best of said encoded signal quality values, said decoderdecodes said encoded signal frame according to the rate associated withsaid selected encoded signal quality value, thereby producing a decodedframe, and wherein said erasure detection unit provides said decodedframe to said host when determining said decoded frame allowed.
 4. Therate detection device according to claim 3, wherein each said pluralityof encoded signal quality estimators processes said encoded signal frameaccording to an encoded quality criteria which is selected from thegroup consisting of: ##EQU37##
 5. The rate detection device according toclaim 3, wherein said controller selects the next best of said encodedsignal quality values when said erasure detection unit does not allowsaid decoded frame, said decoder decodes said encoded signal frameaccording to the rate associated with said selected next best encodedsignal quality value, thereby producing a decoded frame, and whereinsaid erasure detection unit provides said decoded frame to said hostwhen determining said decoded frame allowed.
 6. The rate detectiondevice according to claim 5, wherein said erasure detection unitdetermines said decoded frame as erased after said controller repeatedsaid selecting, a predetermined number of times.
 7. The rate detectiondevice according to claim 3, further comprising:a plurality of decoders,connected in series therebetween and further connected to said host,each for decoding said encoded signal frame at a different rate selectedfrom a second one of said rate-sets, when the previous one plurality ofdecoders failed to correctly decode said encoded signal frame, and arate-set switch connected to said host and before the first of said atleast one decoded signal quality estimator and the first of saiddecoders, for routing said encoded signal frame to said first of said atleast one decoded signal quality estimator, when in a mode according tosaid first rate-set and for routing said encoded signal frame to saidfirst of said at least one decoders, when in a mode according to saidsecond rate-set, wherein a decoder of said plurality of decoders whichsucceeds in producing a correctly decoded frame, provides said correctlydecoded frame to said host.
 8. The rate detection device according toclaim 7, wherein the successes and failure of each said decoders, todecode said encoded signal frame is determined according to an erasuredetection criteria.
 9. In a receiver including a host, receiving anencoded signal frame, the encoded signal frame being encoded in aparticular rate in a given rate-set, the rate-set selected from aplurality of rate-sets, each rate-set including a plurality of rates, arate detection device comprising:a plurality of decoders, connected inseries therebetween and further connected to said host, each fordecoding said encoded signal frame at a different rate selected from afirst one of said rate-sets, when the previous one plurality of decodersfailed to correctly decode said encoded signal frame, wherein a decoderof said plurality of decoders which succeeds in producing a correctlydecoded frame, from said decoding said encoded signal frame, providessaid correctly decoded frame to said host.
 10. The rate detectiondevice, according to claim 9, further comprising:at least one decodedsignal quality estimator, connected in series therebetween and furtherconnected to said host, each for decoding said encoded signal frame at adifferent rate selected from a second one of said rate-sets, when theprevious one of said at least one decoded signal quality estimatorfailed to correctly decode said encoded signal frame, and for producinga decoded signal quality value thereof, at least one encoded signalquality estimator, connected in parallel therebetween and after said atleast one decoded signal quality estimator, for processing said encodedsignal frame, each at different rate of said second rate-set, therebyproducing encoded signal quality values, when all of said at least onedecoded signal quality estimator failed to correctly decode said encodedsignal frame, a controller connected to said at least one encoded signalquality estimator, a decoder connected to said controller, an erasuredetection unit connected to said controller, said decoder and said host,operative according to a predetermined erasure criteria, and a rate-setswitch connected to said host and before the first of said at least onedecoded signal quality estimator and the first of said decoders, forrouting said encoded signal frame to said first of said at least onedecoded signal quality estimator, when in a mode according to saidsecond rate-set and for routing said encoded signal frame to said firstof said at least one decoders, when in a mode according to said firstrate-set, wherein said controller selects the best of said encodedsignal quality values, said decoder decodes said encoded signal frameaccording to the rate associated with said selected encoded signalquality value, thereby producing a decoded frame, wherein said erasuredetection unit provides said decoded frame to said host when determiningsaid decoded frame allowed, and wherein said erasure detection unitrejects said decoded frame otherwise.
 11. The rate detection deviceaccording to claim 10, wherein each said plurality of encoded signalquality estimators processes said encoded signal frame according to anencoded quality criteria which is selected from the group consisting of:##EQU38##
 12. The rate detection device according to claim 9, whereinthe successes and failure of each said decoders, to decode said encodedsignal frame is determined according to an erasure detection criteria.13. In a receiver receiving an encoded signal frame, the encoded signalframe being encoded in a plurality of rates, a rate detection devicecomprising: a plurality of encoded signal quality estimators each havinga different one of said plurality of rates associated therewith, whereineach estimator processes said encoded signal frame according to itsassociated rate, thereby producing a quality value for said associatedrate;a controller connected to said plurality of encoded signal qualityestimators, wherein said controller selects the rate having the bestquality value and provides said selected rate to said receiver, whereineach said plurality of encoded signal quality estimators processes saidencoded signal frame according to an encoded quality criteria which isselected from the group consisting of: ##EQU39##
 14. In a communicationsystem, wherein each transmitted signal frame is encoded in one of aplurality of rates, thereby producing an encoded frame, a method fordetecting said rate, the method comprising the steps of: processing saidencoded signal according to at least two of said plurality of rates,thereby producing an encoded signal quality value for each of saidrates;selecting the best of said encoded signal quality values;selecting the rate associated with said selected encoded signal qualityvalue; decoding said encoded frame according to said selected rate,thereby producing a decoded frame; processing said decoded frameaccording to a predetermined erasure criteria, thereby determining saiddecoded frame either as allowed or as rejected; selecting the next bestof said encoded signal quality values, when rejecting said decodedframe; selecting the rate associated with said selected next bestencoded signal quality value; and repeating from said step of decodingsaid encoded frame according to said selected rate.
 15. In acommunication system, wherein each transmitted signal frame is encodedin one of a plurality of rates, thereby producing an encoded frame, amethod for detecting said rate, the method comprising the stepsof:processing said encoded frame at an elected rate of said plurality ofrates, thereby producing a decoded signal rate quality value, repeatingsaid step of processing for another elected one of said plurality ofrates, when railing to correctly decode said encoded frame or when saidquality value does not exceed a predetermined threshold value,processing said encoded signal according to a plurality of rates,thereby producing an encoded signal quality value for each of saidrates, when failing to correctly decode said encoded frame at selectedrates of said plurality of rates, selecting the best of said encodedsignal quality values, and selecting the rate associated with saidselected encoded signal quality value.
 16. The method according to claim15, wherein each said encoded signal quality value is calculatedaccording to a quality criteria, selected from the group consisting of:##EQU40##
 17. The method according to claim 15, further comprising thesteps of: decoding said encoded frame according to said selected rate,thereby producing a decoded frame, andprocessing said decoded frameaccording to a predetermined erasure criteria, thereby determining saiddecoded frame either as allowed or as rejected.
 18. The method accordingto claim 17, further comprising the steps of:selecting the next best ofsaid encoded signal quality values, when rejecting said decoded frame,selecting the rate associated with said selected next best encodedsignal quality value, and repeating from said step of decoding saidencoded frame according to said selected rate.
 19. In a communicationsystem, wherein each transmitted signal frame is encoded in an electedone of a plurality of rates, thereby producing an encoded frame, thetransmitted signal frame including user data, the user data beingencoded in the encoded frame at a power level which is associated withthe elected rate, a method for detecting the elected rate, the methodcomprising the steps of:analyzing the encoded frame at a plurality ofrates, thereby producing user data power associated quality valuestherefrom, selecting the best of said user data power associated qualityvalues, and selecting the rate associated with said selected user datapower associated quality value, wherein said step of analyzing furtherincludes comparing the user data power of said encoded frame with userdata power of previous analyzed frames.
 20. The method according toclaim 19, wherein said step of analyzing further includes comparing theuser data power of said encoded frame with user data power of previousanalyzed frames, with respect to the rate determined for said previousanalyzed frame.
 21. In a communication system, wherein each transmittedsignal frame is encoded in an elected one of a plurality of rates,thereby producing an encoded frame, the transmitted signal frameincluding user data, the user data being encoded in the encoded frame ata power level which is associated with the elected rate, a method fordetecting the elected rate, the method comprising the steps of:analyzingthe encoded frame at a plurality of rates, thereby producing user datapower associated quality values therefrom, selecting the best of saiduser data power associated quality values, selecting the rate associatedwith said selected user data power associated quality value, decodingsaid encoded frame according to said selected rate, thereby producing adecoded frame, processing said decoded frame according to apredetermined erasure criteria, thereby determining said decoded frameeither as allowed or as rejected, selecting the next best of saidencoded signal quality values, when rejecting said decoded frame,selecting the rate associate with said selected next best encoded signalquality value, and repeating said step of decoding said encoded frameaccording to said selected rate.
 22. In a communication system, whereineach transmitted signal frame is encoded in one of a plurality of rates,thereby producing an encoded frame, a method for detecting said rate,the method comprising the steps of:processing said encoded signalaccording to at least two of said plurality of rates, thereby producingan encoded signal quality value for each of said rates; selecting thebest of said encoded signal quality values; and selecting the rateassociated with said selected encoded signal quality value; wherein eachsaid encoded signal quality value is calculated according to a qualitycriteria, selected from the group consisting of: ##EQU41##
 23. In acommunication system, wherein each transmitted signal frame is encodedin one of a plurality of rates, thereby producing an encoded frame, amethod for detecting said rate, the method of comprising the steps of:processing said encoded frame at an elected rate of said plurality ofrates, thereby producing a decoded signal rate quality value,repeatingsaid step of processing for another elected one of said plurality ofrates, when failing to correctly decode said encoded frame or when saidquality value does not exceed a predetermined threshold value, whereinsaid failing to correctly decode said encoded frame is determinedaccording to an erasure criteria.
 24. The method according to claim 15,wherein said failing to correctly decode said encoded frame isdetermined according to an erasure criteria.
 25. In a communicationsystem, wherein each transmitted signal frame is encoded in an electedone of a plurality of rates, thereby producing an encoded frame, thetransmitted signal frame including user data, the user data beingencoded in the encoded frame at a power level which is associated withthe elected rate, a method for detecting the elected rate, the methodcomprising the steps of:analyzing the encoded frame at a plurality ofrates, thereby producing user data power associated quality valuestherefrom, selecting the best of said user data power associated qualityvalues, and selecting the rate associated with said selected user datapower associated quality value, wherein said user data power associatedquality value is calculated according to a quality criteria, selectedfrom the group consisting of: ##EQU42##